Air blast circuit breaker



Nov. 26, 1-940. D. c. PRINCE 2,222,719

- AIR BLAST CIRCUIT BREAKER Q Filed July 8, 1939 I INSULATION Inventor: David C. Prince, b3 5 His Attbf-he y.

Patented Nov. 26, 1940 UNITED STATES) PATENT OFFICEX AIR BLAST CIRCUIT BREAKER David (7. Prince, Swarthmore, Pa., assignor to General Electric Company, a corporation of New York Application July 8, 1939, Serial N 0. 283,386

6 Claims. (Cl. 200-148) characteristics relating to the rate of increaseof recovery voltage when the current is inter rupted. Although the breaker may be success- 20 increased the dielectric strength of said gap." By

way of example, in a certain instance, a gas blast circuitbreaker interrupted 15,000 amperes in a 13.2 kv. circuit having a recovery rate of 330 volts/microsecond. However, whenthe recovery 25 rate was increased to 1500 volts/microsecond, the same breaker was successful in interrupting but 5,000 amperes under otherwise similar condi= tions. For interrupting higher current under such conditions, it would be necessary greatly 30 to increase the pressure and the intensity of the gas blast or, if it is impractical to increase the gas pressure, theggsize of the blast passage in which the arc is interrupted could be enlarged to provide for greater gas volume. However, 35 such changes would result in either a more ex= pensive or larger breaker.

In accordance with my invention, the inter= rupting capacity of the circuit breaker for a given blast pressure and gas consumption is greatly 40 increased by inserting a suitable resistance in the circuit at a break subject to an efiective gas blast, thereby decreasing the voltage recovery rate of the circuit, and subsequently interrupt ing the greatly decreased current at a much 45 more favorable recovery rate by a comparatively limited blast at another break in series with said first break.

My invention will be more fully set forth in the following description referring to the accom= 60 panying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming apart of this speciflcation.-

Referring to the drawing the single figure thereofis an elevational view partly in section of an electric circuit breaker of the gas blast type embodying the present invention.

The gas blast circuit breaker illustrated by way of example comprises relatively movable contact structure arranged to form two breaks in series at l and 2 respectively upon opening of the circuit. The contact structure specifically shown comprises a pair of fixed contacts 3 and 4 which coact with movable contact members 5 and 6. The movable contacts 5 and-' 6 are electrically interconnected as by a stationary terminal bridging structure I and suitable current transfer contacts 2!. For the purpose of operating the contacts 5 and 6 in unison, they are connected to an insulating member or bar 8 in turn operatively connected to suitable actuating mechanism (not shown). It will be apparent from the above description that opening and closing of the circuit at the points i and 2 can be accomplished by reciprocal operation of m the contact structure 8.

For the purpose of insulating the terminal contacts 3 and 4 and of forming a passage for directing gas under pressure to the aforesaid breaks, an insulating housing 9 is mounted on the terminal structure i for supporting the terminai contacts 3 and 4 in spaced relation thereto. The housing 9 forms two vertically positinned branches to and iiinterconnected by a transverse passage i2 that is in turn connected at M to a suitable source of gas pressure. The contact members 5 and t can, if desired, be made substantially fluid-tight with respect to the lower part oi the housing or bridging ter minai i, and the terminal contacts 3 and 4 fitted as cover members for the vertical extensions i0 and ii oi the housing so that in the closed contact position shown, the housing 9 is for practical purposes substantially gas-tight.

To this end, the stationary contacts are of m the nozzle type so that the movable contact members close the nozzle in the closed circuit position. In the arrangement shown, the nozzle opening of the contact 3 is appreciably more re stricted in cross-section than the opening of the contact ii for a purpose hereinafter described. In order to compensate for the current carrying capacity oi. the contactfi by reason of the comparatively small contact tip 6', auxiliary contacts 5" carried by the member 5 are arranged to contact with the terminal 3 in parallel with the contact tip 5's s For the purpose of facilitating the interruption of a high voltage power circuit characterized by a high recovery voltage rate a resistor 14, the resistance of which depends on the characteristics of the circuit to be controlled, is connected in shunt with the break at I. As shown, the resistor I4 is electrically connected at ii to the terminal contact 4 and at ll to the bridging terminal I. Accordingly. when the contact I breaks contact with 4, the resistance at l4 will be connected across the gap so formed.

The operation of the circuit breaker is as follows. Assuming the breaker to be in closed circuit position shown, the circuit between the line terminals at I1 and II is completed through contacts 1-5, bridging conductor I and contacts 6-4. Lowering of the contact bar I coincident with admission of gas under pressure to the housing 8 by way of conduit It causes initial separation of the contacts 4 and 6 together with a gas blast through the stationary contact .4 opening 4. An eilective arc interrupting blast at the proper blast pressure takes place when the contacts are separated but a short distance. such as approximately two centimeters. At this point, the contact 5 is still in engagement by reason of the longer extension tip 5' so that the arc is conflned to the gas blast between contacts 4 and B. At a current zero, the arc is interrupted and the resistance i4 automatically inserted in the circuit. The high velocity gas blast now prevents reestablishing oi the arc. The line current and also the voltage recovery rate are thereby greatly reduced by the resistance so that upon separation of the contacts I and 5 immediatelythereafter, the greatly reduced gas blast at the nozzle opening of the contact 3 is quite sufllcient to extinguish the low current arc. This second interruption completely opens the circuit with a minimum expenditure 01 gas blast energy. The breaker can be comparatively compact in design since large blast openings and contact structures are not required for high current interruptions.

Although sequential operation of the contacts at the two breaks is preferred, such operation is not entirely essential as the breaks may be formed simultaneously.

The control of the gas blast by suitable valve means forms no part of the present invention and is omitted in the interest of clearness. It will be apparent however that such control may be in response to the usual relay operation or in accordance with the movement of the contacts as desired.

It should be understood that my invention is not limited to speciflc details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire 'to secure by Letters Patent of the United States is:

1. An electric circuit breaker comprising relatively movable contact structure arranged to form a plurality of breaks in series, a resistance connected in shunt with one oi said breaks, means for initially opening the circuit at said resistance shunted break, means for directing a fluid blast through said resistance shunted break to interrupt arcing thereat, and means for directing a second comparatively restricted fluid blast through another series break for flnally interrupting the circuit.

2. An electric circuit breaker comprising relatively movable contact structure arranged to iorm a plurality of breaks in series, at least two of said breaks being iormed in fluid passages, a resistance connected in shunt with one of said breaks, means for initially opening the circuit at said resistance shunted break, means for directing a fluid blast through the passage at said resistance shunted break to interrupt arcing thereat, and means for directing a second fluid blast of appreciably lower intensity through the passage at the subsequently iormed series break for flnally interrupting the circuit.

3. An electric circuit breaker comprising relatively movable contact structure arranged to form a plurality of breaks in series, at least two of said breaks being formed adiacent to the exhaust portions of separate fluid passages, a resistance connected in shunt with one oi said breaks, means for initially opening the circuit at said resistance shunted break, means for directing a fluid blast through the passage at said resistance shunted break to interrupt arcing thereat, and means for directing a comparatively restricted second fluid blast through the passage at the subsequently formed series break tor flnally interrupting the circuit.

4. An electric circuit breaker of the gas blast type comprising a pair of flxed contacts and coacting movable contact members arranged to form two breaks in series, a resistance connected in shunt with one of said breaks, means for directing a gas blast through the are formed at said resistance shunted break for inserting said resistance in the circuit, and means for directing a gas blast of less magnitude through the other break for flnally interrupting the circuit.

5. An electric circuit breaker oi the gas blast type comprising a pair of flxed contact structures forming two separate gas blast passages, one of which is restricted in cross-sectional area as compared with the other, coactingmovable contacts normally closing said passages in the closed circuit position and arranged to form with said flxed contacts two breaks in series, one oi said movable contacts being ada'ptedi to separate in advance of the other movable contact, a resistance connected in shunt with the break thus initially formed for reducing the rate of increase of recovery voltage of the circuit, and means ior directing a gas under pressure to said passages for interrupting arcing at said initially formed break and thereby causing insertion of said resistance in the circuit, said gas under pressure subsequently interrupting the circuit at said restricted e.

6. Electric circuit interrupting means of the gas blast type comprising a pair of relatively movable contacts, means iorming'a gas passage in which said contacts separate, means for directing a gas blast of suilicient magnitude through said passage to interrupt a high current power are upon separation of said contacts, a resistance connected in shunt with said contacts for reducing the line current upon interruption oi said are, a second pair 01' contacts connected in series with said first-named pair, means forming a second gas e in which said contacts separate, and means for limiting the magnitude of the gas blast at said second passage as compared with said flrst passage for interrupting the aforesaid reduced line current.

DAVID C. PRINCE. 

